Steering wheels, because of their convenient location, typically include switches that actuate various motor vehicle accessories. Automobile horn switches are the most common of these. Traditionally, these horn switches have been relatively large buttons centrally located at the hub of the steering wheel. Their large size simplifies the operator's task of quickly locating and depressing the switch. See, for example, U.S. Pat. Nos. 4,575,117, issued Mar. 11, 1986 to S. Uchida, 4,612,425, issued Sep. 16, 1986 to M. Kanai et al., 4,638,131, issued Jan. 20, 1987 to R. L. Kidd et al., and 4,714,806, issued Dec. 22, 1987 to S. Inui et al.
Steering wheels are also the most convenient location for mounting a driver's side air bag. The air bag is often mounted at the hub of the steering wheel. However, the incorporation of an air bag unit within the steering wheel has made the inclusion of horn or other actuating switches within the steering wheel more complicated. Firstly, the air bag unit with its casing and cover door occupy a significant portion of the area within the steering wheel rim. Secondly, the cover door must be free to open upon expansion of the air bag.
Consequently, the horn switch has typically been relocated away from the hub and downsized to fit within the remaining space within the rim about the air bag cover door. See, for example, U.S. Pat. Nos.: 3,819,205, issued Jun. 25, 1974 to S. G. Dunford et al., and 4,325,568, issued Apr. 20, 1982 to H. D. Clark et al. However, due to the historically conventional practice of locating a horn switch at the hub of a steering wheel, most drivers still feel more comfortable with a horn switch at the hub, particularly when faced with a panic situation. The conspicuous presence of a large pad at the hub further confuses drivers into mistakenly believing that the pad is the horn button.
Various arrangements have been disclosed for providing membrane switches incorporated into air bag cover doors to thereby return the location of the horn switch to the hub. See, for example, U.S. Pat. Nos. 4,934,735, issued Jun. 19, 1990 to J. T. Embach; 5,002,306, issued Mar. 26, 1991 to T. Hiramitsu et al.; and 5,062,661, issued Nov. 5, 1991 to L. J. Winget. These membrane switches are composite structures which typically include a flexible member covered by a conductive surface which is separated by a spacer from another conductive surface. The multiple components used in these switches (i.e., the first and second conductive surfaces, flexible membrane, and spacers) increase the complexity of manufacturing the air bag cover door.